W123 300 coupe rear window

Doing online research about rear window problems ( not rolling all that way down) I've found that is a very common problem, however, answers never seem to be accurate on how to approach the problem, some guiding towards regulators, others to switches etc .

My own problem is that window stop rolling down , when is 3/4 open and 1/4 left to be totally .

Can you please share some data base on your experience at this matter ?